Studies on acquired systemic resistance in mice with oral immunization with Shigella sonnei.

Virulent, viable Shigella sonnei bacilli introduced orally, induced in mice resistance against lethal intravenous (i.v.) infection with dysentery bacilli. The immunized animals survived lethal infection and also bacilli were effectively destroyed in the spleen and liver of the immunized animals. It was shown that orally induced immunity may be transferred into nonimmunized mice by means of serum and spleen cells taken on definite days after immunization of donors. Protective activity of serum appeared to be dependent on the presence of specific antibodies and was correlated with their titer. Protective activity of spleen cells occurred about 6 days after immunization of the cell donors with the bacilli. Cell suspensions, prepared from the spleens taken from donors on day 6, protected 100% of the recipients of these cells from lethal infection. Results of these studies indicate that bacterial infection developing in the intestine mobilizes besides local immunity also general immunity. Mechanism of the general immunity induced by orally administered dysentery bacilli is discussed.